Metering pump



Jan. 20, 1959 w. H. KREAMER METERING PUMP Filed March 15. 1954 UnitedStates METERING PUMP William H. Kreamer, Roanoke, Va., assignor toAmerican Viscose Corporation, Philadelphia, Pen, a corporation ofDelaware Application March 15, 1954, Serial No. 416,269 1 Claim. (Cl.103-126) This invention relates to gear type liquid pumps and, moreparticularly, to a precision gear pump used for metering liquids.

I have found that pumps of the type used to meter viscose and othersimilar fluids from which synthetic textile sheets, films or filamentsare spun sometimes cause bubbles in the metered fiuid stream. Thesebubbles are highly undesirable since they result in broken filaments.Elforts to eliminate the bubbles in metering pumps of this type haveincluded the expedients of supplying the viscose to the pump undervarying degrees of pressure and also the provision of various reliefgrooves and ports in the pump plates. All previous designs for suchpumps with which I am familiar have proceeded on the theory that it wasnecessary to provide a pressure relief groove on the delivery side ofthe pump in order to permit fluid trapped between the incipientlymeshing teeth of the gears to be discharged through the relief passagesand thence into the delivery chamber. Such relief grooves are well-knownin the art and have extended in the direction of gear travel towards thecenterline of the gears to a point at which the gear teeth are nearlyfully meshed. This insures that substantially all of the liquid trappedbetween meshing teeth has been forced out of the teeth which in turnprevents rough running of the pump.

On the intake side of the pump, it has been proposed to use one or moresuction relief grooves which connect the intake chamber and/or port withthe disengaging gear teeth before they are completely unmeshed. Other-Wise, the disengaging teeth tend to create a vacuum or low pressure areabefore any of the intake fluid is delivered to the chamber whichincreases in volume as the teeth disengage. Hcretofore, such suctionrelief grooves have not extended beyond the centerline to the pressureside of the pump because the effective seal created at the centerlinewould be thereby reduced or destroyed.

I have found that it is possible to eliminate the pressure relief grooveand also to eliminate the possible formation of bubbles in the liquid bymoving the suction relief groove beyond the centerline of the pump sothat the suction or intake chamber of the pump is in communication withthe chambers formed in the gear teeth at a point which is the same orslightly after the point at which these chambers between the teeth areclosed. The invention also includes the provision of enlarged chambersfor liquid trapped between the gear teeth. These enlarged chamberscooperate with the location of the suction relief grooves in reducingthe percentage of volume change which occurs in the teeth chambers.Heretofore, the teeth of metering pump gears have been so accuratelymade that practically full scavenging of the teeth chambers isaccomplished at the centerline. In other Words, practically no liquid iscarried past the seal.

A principal object therefore of the present invention is to provide, ina metering gear type pump, a relief groove passage 26 and intake port27.

Fatented Jan. 20, 1959 or channel which extends beyond the centerline ofthe gears towards the delivery side of the pump.

A further ob ect of the invention is [0 provide a passage Whit/.1COillIIlLullCaLBS between the intake chamber of a ear pum al'iu thechambers tormed between teeth of ...e lTlcSl'llllg gears at a point onthe pressure side of the pump at or ust after cut-off occurs between theteeth chambers and the delivery chamber.

A further object of the invention is to provide undercut teeth in a geartype pump in which the intake chamber is in fluid communication with theundercut chambers on the gears on the pressure side of the pump.

Further objects will be apparent from the specification and drawings inwhich:

Figure l is an exploded view of a gear type metering pump constructed inaccordance with the present invention;

Figure 2 is a face view of one of the pump plates shown in Figure 1;

Figure 3 is a face view of the other of the pump plates shown in Figure1; and

Figure 4 is a highly enlarged fragmentary detail showing the location ofthe suction relief groove with respect to the meshing teeth and thecenterline.

The invention comprises essentially the provision of a relief groove orpassage extending from a point beyond the centerline of the pump gearsto provide limited fluid communication between such point and the intakechamber. In addition to such a groove or grooves, the teeth of the gearsare shaped to permit a substantial amount of trapped liquid to becarried past the centerline of the pump.

Referring now more particularly to the drawings, a gear pump constructedin accordance with the present invention and intended for use as ametering pump for liquid viscose and similar materials has a front sideplate 10 and a rear side plate 11. These two plates are securely clampedtogether when the pump is assembled by means of machine screws 12, 12.The space between the plates when assembled is partially filled by thedriving pump gear 13 and the idler pump gear 14 which turn in thehousing plate 15. Guide pins 16, 16 and spacing collars 17 on each pinprovide the desired alignment and structural rigidity for the pumpassembly. The shaft 29 which is connected to and drives gear 13 extendsthrough an aperture 21 in front plate 10 and an aligned aperture 22 inrear plate 11. ldler gear 14 is journaled on a pin or post 23 mounted inplate 11. The gears 13 and 14 turn, in the present instance, as shown bythe arrows in Figure 1 so that the intake chamber is partially boundedby the concave cut-away face 24 in the plate 15. Fluid intake to thechamber is provided through the customary orifice 25 in plate 10 whichcommunicates with a drilled The discharge chamber is partially definedby the concave face 28 on the opposite side of housing plate 15. Fluidis discharged from the pump through an orifice 29 which connects withthedischarge chamber through a drilled passage 30 and discharge port 31.The structure described above is substantially conventional in pumps ofthistype and therefore forms no part of the present invention.

It will be especially noted that the intake chamber (not shown as wouldappear with the pump assembled,

strictly necessary depending upon the viscosity of the fluid pumped, thepressure on the intake or supply fluid, and the depth and size of thepassages. It will be noted, however, that particularly the groove 35,which is in communication with the intake port 27, extends beyond thecenterline C of the gears as shown clearly in Figures 3 and 4. This, ina sense, introduces intake fluid to the discharge side of the pump asdefined by the centerline between gears 13 and 14. Notch 36 likewiseextends somewhat beyond the centerline as shown in Figure 2. The reasonfor this location of either or both of the notches 35 and 36 will bemore apparent in connection with the description of Figure 4. Inaddition to the provision and location of the grooves 35 and 36, Iundercut the teeth of both gears to provide chambers or passa es for theentrapped liquid as the gears fully mesh. The advantages of thesepassages in the gears or between the gear teeth are be ieved to be inthe substantial decrease percentagewise of the compression present inthe volume of fluid carried past the seal or centerline of the gears.Furthermore, these passages assist in eliminating the release of airbubbles in a fluid such as viscose by acting as miniature expansionchambers.

Referring now more particularly to Fi ure 4. it will be seen that tooth14a has just sealed the liquid in chamber 37 between teeth 13a and 13!).This is by reason of the line contact at 38 between teeth 13a and 14a.Chamber 37 is. at this instant, filled with liquid at substantially thedischarge pressure. As the gears continue their turning in the directionshown by the arrows. tooth 14a would ordinarily compress the liquid inchamber 37 because it continues in sealing contact with both of theteeth 13a and 1.3!; while simultaneously entering farther into thechamber 37. However. it will be noted that substantially at or slightlyafter the instant that sealing contact is made at 38 between teeth 13aand 14a chamber 37 is opened to communicate with groove 35 at 39. Thisis achieved by extending the groove 35 beyond the centerline to thepressure side of the pump as noted above and sufliciently far that thegroove 35, in effect. acts as a pressure relief groove. As the gearscontinue to turn. the minimum volume of chamber 37 will be reached. Sucha condition is illustrated with respect to chamber 40 which is shown inFigure 4 with tooth 13!) directly on the centerline. However, at thispoint chamber 40 is com letely in communication with the intake port 27through either or both grooves 35 and 36. It will thus be seen that notonly was there no opportunity for excessive pressure to build up causingroughness of the pump, but the early fluid communication between teethchambers and the intake chamber tends to equalize any pressuredifferences in the chamber.

Ordinarily, as the gear teeth pass beyond the centerline and disengage,there is a tendency to create a vacuum or a low pressure condition inthe chambers, if any, between the teeth. Thus it will be seen thatchamber 41 is of substantially greater volume than chamber 40 and, infact, equal to chamber 37. However, this increase in volume, as shown atchamber 41, does not create a low pressure condition therein even thoughthere is still a seal at 42 between teeth 13c and 141; because chamber41. is in fluid communication with the intake chamber and liquid throughgrooves 35 and/or 36. Of course, as soon as the seal 42 is broken, asshown between teeth 13c and 140, the tooth chambersuch as 43 is in fullcommunication with the intake chamber 24. It will thus be seen that thelocation of the groove 35 as shown in Figure 4 provides a pressurerelief to inhibit pressure rise in the fluid trapped between gear teeth.It does not, however, adversely affect the seal between the teeth sincethere is no point at which direct communication takes place through theteeth between the pressure and intake chambers of the pump. Groove 35also inhibits any decrease in pressure in the teeth chambers as theteeth disengage, and therefore there is no time nor opportunity forexcessive pressure to be built up which would tend to form bubbles whenreleased.

It will be understood that the shape and location of the relief grooveor grooves can be varied substantially within the scope of theinvention. However, any further positioning of the grooves to the right,as shown in Figure 4, would sharply decrease the pump capacity due tothe loss of a seal. Should it be desired to restrict the righthandterminus of the grooves, as seen in Figure 4, so that the teeth chamberswould be opened at about the centerline there would, of course, then besome pressure build-up in chambers 37, 40, 41 and 43. This would moreeffectively seal the pressure and intake chambers but might result inslight rough running. The tendency under these conditions, however, toproduce bubbles would be minimized because the percentage reduction involume of chambers 37, 40, 41 and 43 would be much less than where theconventional non-undercut gear tooth is used.

Having thus described my invention, I claim:

A metering gear pump for pumping viscous fluids comprising a pair ofpump side plates, a pair of meshing gears mounted between said sideplates, each of said gears having cut-away portions between the teeththereof whereby chambers of substantial volume are formed at the pointof full meshing engagement of the teeth of the gears, a housing platesecured between the side plates and closely embracing the major portionof the peripheries of said gears, said housing plate and said sideplates cooperating to form a suction chamber on one side of thecenterline of said gears and a pressure chamber on the other side of thecenterline of said gears, an intake for viscous fluid extending througha first one of said side plates and communicating with said suctionchamber, an output port in the other of said side plates communicatingwith said pressure chamber, and a circular indentation in the inner wallof said first one of said side plates, said indentation encompassing anarea aligned with the intake, the chambers formed at the point ofcomplete meshing engagement of the gear teeth and the suction chamber.

References Cited in the file of this patent UNITED STATES PATENTS1,129,090 Hawley Feb. 23, 1915 1,348,773 Auger Aug. 3, 1920 1,719,025Scheminger, Jr July 2, 1929 1,863,160 Jensen June 14, 1932 1,891,793Kaulfman Dec. 20, 1932 1,976,227 Howard Oct. 9, 1934 1,985,748 SvensonDec. 25, 1934 2,281,767 Heckert May 5, 1942 2,498,790 Caughrean Feb. 28,1950 2,540,235 Berkley Feb. 6, 1951 FOREIGN PATENTS 366,152 Germany Dec.30, 1922 421,373 Germany Nov. 10, 1925

